The use of rolled web (e.g. paper) in conjunction with a digital printer and various peripherals (e.g. cuttings, slitters, folders, stackers, etc.) has become a ubiquitous technique for producing a variety of printed materials. A typical web-handling/printing arrangement involves the use of a web unwinder, which can be driven at its core and/or its outer perimeter, and which passes through the various web-handling peripherals. The output web from the peripheral(s) can then be rewound, by a core-driven, or surface-driven rewinder onto an output web roll. This web roll can be used in further handling processes (e.g. further printing, cutting, stacking, folding, etc.). Typically one or more (e.g. dancer) loops are present between the components of the system, typically to sense the demand for web at input and output of the components. The size of the loop is used to speed or slow the rotation of unwinder and/or rewinder. The loop contains a sufficient festoon of web so that the amount of web therein can absorb any unevenness in web flow the acceleration and deceleration of the unwinder/rewinder. This generally avoids over-tensioning of the web and damage to components.
The trend in this industry is toward heavier paper stocks and higher web speeds (e.g. 500 fpm or more). This combination of factors engenders a scenario in which the web is under enormous tension in the event of a sudden stoppage. In the event that amount of web stored in the festoon (loop(s)) between components becomes exhausted (taken up) before the slowly decelerating rewinder (which is reacting to an emergency stop condition by shutting down) comes to a full stop, then the flywheel energy generated by the spinning web roll(s), combined with a very strong web, transmits substantial forces back through the rewinder and into the output end of the printer/peripheral, as that web becomes suddenly taut.
It is desirable to provide a mechanism that avoids the potential damaging effect of a heavy, taut web during an emergency stoppage of the printer or other peripheral interconnected to a rewinder, or a stoppage/jam within the feed path of the rewinder itself.